Apparatus for casting under pressure in dentistry



. K. INAMI` APPARATUS P'ORl CASTINGUNDER PRESSURU Ill lDENTISTRY Filed 0M.. 31.-. 1.9225` -muuu-mln Patented Jan. 3l, 1928. i j

UNITED STATES Pian-:rrr OFFICE.

KAKUJ'IBOINAHI, 0F IKASHIWAGI, J'PAN'.

APPARATUS FOR CASTING UNDER `EPBESSU'IRE IN DENTISTRY. I

Application led October 31, 1925. Serial No. 88,041.

I castings of exact size and constructed to re' quire but a short heating and to facilitate the rapid esca-pe of gases. v

The apparatus now in use, while lessun- "sirable for small castings than for large cast-ings, has many disadvantages when employed in the preparation of castings requiring accurate measurement and surfaces free from roughness. Becauseof the shortcomings of the apparatus as well as the dliculties encountered in adapting the apparatus to work of an exact nature, the castings pro-v duced are usually thicker than the wax pattern, rough surfaced, and more or lessdeformed so that they do not fit properly.

Sometimes, the castings are so badly formed as to require several recastings before a' good specimen is obtained.

Hitherto the practice has been to form a mould by pushing the prepared Wax pattern into the plastic investment compound and allowing t-he latter to set after it has completely surrounded the pattern. The preparation of the attern is usually done on a. model. Since t c wax is soft, removal from the model and subsequent handling preparatory to inserting the attern in 4the investment compound invaria ly resiilts in deformation of the pattern.- Then,jl as the compound set/s, the pattern is further deformed because of the shrinkage of'fthe compound, and cracks are formed 1n the surface of the mould. If the mould is` formed with a small number of comparative! thick sprues,.because of the nature ofgthe flaskfthe 40. bulk of the casting metalis increased and the amount of shrinkage is very large and the resulting casting is considerably distorted. On the other hand, if the crucible formed in the top of the flask is too shallow vsufi-.icient metal rcannot be' properly kept in its molten stageand all parts of the mould will not be filled.

To overcome such diiliculties `as havebeen pointed out, I have constructed apparatus for successfully preparing dental castings of exact size with even surfaces. The various features of my apparatus when applied in the preparation of the upper jaw denture,.as

an example, are illustrated in the following drawings whereinl Fig. 1 is a perspectiveview of a wax pattern of the denture in position on its model block, 9

Fig. 2 is aperspective view showing how the plastic investment compound is poured around the pattern,

Fig. 3 is a perspective View of the cast formed by thevinvestment compound,

' Fig. 4 is a sectional perspective view showing the wax pattern imbedded in the cast- 05 ing mould,

Fig. 5 is a sectional perspective view of the wax pattern after the model block has been removed,

6 is a perspective view of a flask,

F1 7 1s a perspective view of a pouringl cruci le pattern,

.F1g. 8 is a vertical sectional view showing the casting mould,

Fi 9 is a vertical sectional view showing the ask in a heater,

Fig. 1Q is a vertical .sectional view showing the apphcation of pressure during the castlng operatlon.

In the accompanying drawings, a model of .an upper jaw cast of plaster, artificial stone, or othersuitable material is shown at a. A pattern of a gold plate to be cast, shown at b, is formed by pressing `wai: sheets of the proper thickness upon the surface of the model a. U-shaped wax wires c, which later form shoulders for the vulcanite backing of the denture, are arranged and attached around the outer .edge ofthe pattern b. A plurality of slender wax wires d, for forming sprues, are attached at their one end to the U-shaped' wax' wires c as Well as to other parts of the pattern b, and arc bunched together at their other end in order to form a closely arranged group of pouring holes. Surrounding the pattern b and secured to .theJmodel block a is a shell e into whichis pouredthe castin compound. The grouped wires d project rom the apexJof the shell, as shown in Fig. 2.

With the shell e in the position yshown in Fig. 2,v investment compound of the proper consisteilcy ispoured in through the openinguin the upper side. The compound is care lly packed around the wax attern and wires and then' allowed. to garden. After the compound has set, the shell e and model block a. may be removed and .the l mold M turned'with the wax pattern to the top, as shown in Fig. 4. The surplus mai# -crucible pattern, as explained later. l0

A flask adapted to receive the pyramidal mould M and consisting of a cylindrical part i, lattice portion j, and semi-elliptical rim z' is shown at F in Fig. 6. The cylindrical collar serves as a seat for a pouring Crucible pattern. The semi-elliptical rim is considerably larger than the cylindrical collar in order to accommodate the large end of the mould M. To facilitate the' escape of gases, rods j are used to connect the collai' `and rim and provide the openings lo through which the gases can readily pass during heating. A pouring crucible pattern P, illustrated in Fig. 7, is provided with a conical projection 11, and a shallow groove fm, on its one face. The groove is of such a size as to fit over the collar i, of the flask while the opening 0 in the conical portion has a diameter equal to the small end of the mould M.

To assemble the mould M in the flask F, as shown in Fig. 8, the flask is inverted upon the crucible pattern P and a paper or rubber guard p placed around the `lattice bars y'. The mould M is then placed in the flask With the small end of the mould projecting into the hole 'o in the Crucible pat' tern. Investment compound ofthe proper consistency is slowly Worked into the flask and around the mould until the flask is filled to the rim z'. The mould M is thus completely surrounded by the compound with the exception of the small portion at the apex. After the compound has hardened, the guard paper p is removed and the Crucible attern taken 0E, the portion of the mould extending through the hole being broken olf when the attern is removed.

rlhe preparation o themould for casting is thus carried out in three stages. First,

`the investment compound is applied to the wax pattern positioned on the model block. When the compound has hardened, the model block is removed, and the cap portion of investment compound added. After the 4cap portion has hardened, the entire mould M is inserted in the flask and packed with further investment compound. Considering the effect ofthe several stages upon the wax pattern, when the shrinkage of the first. application of compound f tends to deforin the wax pattern such action will be prevented by the rigidity of the model block. Thenwhen the shrinkage of the cap portion of compound tends to defoi'in the pattern, deformation will be prevented by the hardened compound portion f. The lwai: `pattern is thus not influenced by the shrinkage of the various layers of the investment compound. After the mould is packed in the flask and heated to the necessary high temperature, fissures are produced in the compound because of its nature, but such fissures do not alter the rela tive position of the two parts of the mould M. Furthermore, since the cap portion g is locked upon the portion f by reason of the overlapping edges, no movement between the two parts will occur due to the expansion and contraction of the compound.

'lhe'iilled flask is placed iii a heater, as shown in Fig. 9, with the crucible upward and heated, slowly at first and gradually stronver until the mould is dry. After the mould is dry the heat is continued from the Bunsen burner until the wax wires and pattern have completely vaporized and passed up out of the mould, leaving the pattern cavity '1 and the spiues s. The mould is then ready for casting.

At this stage, if the metal to be used for the casting is one having a low melting' point, such as aluminum, the casting work can'be commenced immediately. If gold is used, however, the mould must be heater still further. To raise the heat to the point necessary, charcoal is piled around the flask and both Bunscn and charcoal burned together. When on looking through a peep hole 1/ in the lid a: of the heater the flask is seen to be .heated red hot, the upper portion t of the heater is removed and a lid o; placed over the remaining portion u as shown in Fig. 10. The desired metal is then placed in the Crucible and smelted with a torch as indicated. When the metal is completely melted and running into the spi'nes, a pressure lid lV or other pressure means, is placed over the Crucible. Under the pressure thus formed, the molten metal completely fills the cavities in the mould and produces a coinpact and smooth surfaced casting of the saine size as the wax pattern Z).

Because the greater part of the flask is 'formed of open lattice work, the escape of gases, either existing or generated during casting, is greatly facilitated with the result that the formation of cracks and bubbles in Vthe surface of the cavity substantially lll() llU tributed throughout the cavity, the molten metal flows steadily and quickly into the mould Without forming irregularities in the casting. Numerous small sprues are far better than a few large sprues because the thin casting is less apt to be affected by the shrinkage of the small amount of metal contained in the small sprues than by the shrinkage of the large quantity of metal contained in the large sprues. rlhen too, a large numberof sprues can be better distributed over the casting. Because of the simplicity of the apparatus the heating means need not he extensive. rlhe heater can be constructed and operated very inexpensively and is not excessively injurious in its effects upon the llask. Either gas or charcoal may be used in the heater by virtue of its sturdy construction.

lt is to be understood that various modifications may be made in the apparatus as described and illustrated Without departing from the spirit and scope of the invention as defined by the following claims.

l claim:

l. ln casting apparatus for dental prosthesis, a moulding fias'k comprising a collar portion, a rim portion larger than said collar portion, a lattieed portion intermediate and joined to said collar and rim portions, and means adapted to tit over said collar portion for positioning a mould in said iiask 2. ln casting apparatus for dental prosthesis, a moulding flask comprising a cylindrical collar portion, a semi-elliptical rim vportion larger than said collar portion,a

latticed .portion joined to said collar, and rim portions and forming a frusto-conical enclosure, and means adapted to lit over said collar portion for positioning a mould in said flask.

3. ln casting apparatus for dental prosthesis, a moulding flask comprising a collar portion, a rim portion, a latticed portion joined to said collar and rim portions, and a cover for said collar portion, said cover having an inwardly projecting conical portion adapted to position a mould in saidA flask.

l. ln casting apparatus for dental prosthesis, a moulding flask comprising a collar portion, a rim portion, a latticed portion joined to said collar and rim portions, and a cover for said collar port-ion, said cover having an inwardly projecting conical porr tion adapted to position a mould in said liask and to form a pouring Crucible therefor when said flask is filled.

ln casting apparatus for dental prosthesis, a moulding flask comprising a collar portion, a rim portion, a latticed portion joined to said collar and rim portions, and

a cover for said collar portion, said cover4 having a central hole, a conical projection surrounding said hole and extending from one face of said cover, and a groove in said face concentric with said conical portion.

ln testimony whereof l atiix my signature.

KAKUJ IRO INAMI.

STI 

